1. Field of the Invention
The present invention is related to medical diagnostic equipment and, more particularly, is directed towards a self-contained cardiac monitor which is adapted to be incorporated into a standard electronic digital wristwatch to perform concurrently therewith.
2. Description of the Prior Art
Much of the heart research being conducted today is directed toward the many clinical aspects of cardiac disease. That is, such research is directed toward uncovering information that will lead to lowering the risk of heart attacks, surgical correction of heart defects and abnormalities, and restoration of the heart patient to an active life.
In contrast, and unfortunately, very little attention in research has been paid toward the vital aspects of early detection and management of heart malfunction and disease. If a convenient and simple early detection and warning system of impending heart disease could be developed and were widely utilized, it would lead in most cases to early treatment which could prevent or delay progress of the condition.
For example, one of the most prevalent heart diseases is an outgrowth of a condition known as hypertension. Factors such as excitement, fear, frustration, and the like, all affect hypertension in varying degrees. If the onset of hypertension could be simply and accurately determined by the individual at any time, appropriate corrective action may be taken before the damage is done.
In that regard, it is important in the development of any useful cardiac monitoring system that it be enabled to respond rapidly to a sensed change in the individual's cardiac characteristics. Obviously, a system with a slow response, i.e., one which fails to notify the user at the onset of the condition, is of extremely little value.
Another factor of great importance to consider in designing and developing a suitable cardiac monitor is that it be convenient to utilize. This requirement is often translated into requirements that the device be portable, rugged, convenient, and relatively inexpensive to manufacture. Further, such a device, if it is to be utilized to maximum value, must be always in a state of readiness to detect the onset of any irregularity or variation. Thus, it must be incorporated into a device which is readily and unobtrusively worn by the individual user or patient.
Naturally, in such a cardiac monitor, a suitable indication or alarm must be given upon the detection of a malfunction or irregularity so as to alert the individual user thereof.
Prior art patents of which we are aware in this field include: Manuel et al. U.S. Pat. No. 3,838,684; Greenwood U.S. Pat. No. 3,717,140; Orr et al. U.S. Pat. No. 3,807,388; and Hokanson U.S. Pat. No. 3,777,740. Each of the foregoing patents describe cardiac monitoring devices which incorporate various techniques for monitoring the pulse or heartbeat. For example, the Manuel et al, Greenwood, and Orr et al devices utilize pressure sensitive transducers for picking up the pulse beat.
Another technique utilized in cardiac monitoring systems utilizes photo-optic transducers. Such transducers are not as sensitive to noise movement as are the pressure sensitive devices discussed above, although they are still subject to receiving false pulses. However, the basic disadvantage of utilizing photo-optic transducers as the pulse pick-up system lies in that extensive applied pressure is required in order to develop correct readings from the wrist of the user. While photo-optic devices are widely used with respect to an individual's fingers, such a device would be unduly obtrusive and not readily worn continuously. In order to render such photo-optic transducers amenable to wrist-worn devices, therefore, a special wrist restraint device must be developed and utilized. Additionally, photo-optic transducers require excessive current drain that leads to short battery lifetimes and concomitant high expense.
Since the design of the pulse pick-up system is undoubtedly critical to the operability and accuracy of a working cardiac monitor, several additional techniques were investigated. For example, microphone transducers were found to produce as much noise as the pressure sensitive transducers and were therefore rejected. Microwave transmission and detection can result in a danger to the health of the patient resulting from accumulative radiation. Further, there is a possibility of deleterious interaction of the microwave with other cardiac equipment, such as the widely used Pacemaker. Thus, microwave transmission and detection was considered and rejected. Finally, capacitive detection was attempted but was found to have an accuracy dependent upon changes in temperature and humidity which therefore led to the rejection of this type of pulse pick-up system.